Chapter 6. Microscale Gas
Chemistry:

Ammonia
is a colorless gas with a sharp, irritating odor. It is extremely
soluble in water and is lighter than air.

B. Physical Properties
of NH3

Ammonia, NH3

Atomic mass:

17.0306 g/mol

melting point

-77.7 oC

boiling point

-33.3 oC

C. History
Ammonia was first isolated by Priestley in 1774 with the aid of a pneumatic
trough filled with mercury instead of water.

D. Natural Abundance
Ammonia is produced by the anaerobic decay of organic material. Ammonia
was the first complex molecule to be identified in interstellar space and
solid NH3 makes up the rings on Saturn.

E. Industrial Production
Prior to the 20th century, ammonia was made by destructive distillation
of animal parts such as hoofs, horns, etc. The common name for ammonia
was “Spirits of Hartshorn.” In 1913, Haber worked out a synthetic
route to catalytically produce ammonia from the elements at high pressure
and temperature. The Haber process is still used today.

N2(g)
+ 3 H2(g) ---> 2 NH3(g)
DH = -92 kJ
DS = -199 J/K

F. Industrial Uses
Ammonia production is the largest consumer of nitrogen and is the gateway
compound to most other nitrogen compounds produced industrially.
Enormous quantities of ammonia are produced worldwide. Much of the
ammonia produced in the USA is used directly for fertilizer. The
figure below shows the various uses of ammonia. The majority of all
ammonia and ammonium nitrate producted is for use as fertilizer.
Approximately 70% of all NH3 produced is directly
used for fertilizer. Farmers inject the pressurized liquid ammonia
into the soil. Ammonia is so soluble in water and has such a high
affinity for polar groups such as hydroxyl groups that the ammonia is almost
instantly taken up by the soil and very little is lost to the atmosphere.

Other important
uses of ammonia include the production of nitric acid, use as a refrigerant,
and use as a non-aqueous solvent. Ammonia’s use as a refrigerant
comes from the fact that it is a condensable liquid. Ammonia is currently
commonly used as the refrigerant in large industrial refrigerators and
freezers. Its main disadvantage in residential use stems from its
toxicity should a leak in the system develop. Liquid ammonia is also
the most common, widely used non-aqueous solvent. Its boiling point,
-33.3 oC, requires that vessels be refrigerated or pressurized.
Ammonia is used in the manufacture of numerous other chemicals and products
ranging from dyes to plastics.

G. Gas Density of NH3
The density of NH3 is 0.6826 g/L at 25 oC
and 1 atm. This is about half that of air’s, thus it tends to rise
in a still room.

H. Gas Solubility of NH3
Ammonia is extremely soluble in water. As much as 89.9 g dissolve
per L at 0 oC. This means that 1
mL of water will dissolve 1183 mL ammonia! At 100 oC,
the solubility drops to 7.4 g ammonia /100 mL H2O
(113 volumes NH3 per 1 volume water.)